The present invention relates to a fishline tension measuring device for a fishing reel, which measures tension applied to a fishline using an electrostatic capacitance sensor.
The present inventor, Mr. Hirose, has previously disclosed in Japanese Utility Model Kokai Publication No. Sho. 64-5493 a fishline tension measuring device for fishing reel, capable of measuring the tension caused on a fishline by use of a strain gage when fish is caught in the terminal tackles of a fishing reel.
FIGS. 12 to 14 respectively show the fishline tension measuring device that is disclosed in the above-mentioned publication. The fishline tension measuring device will be described below with reference to FIGS. 12 to 14.
In particular, FIG. 12 is a partially cutaway front view of the above disclosed fishline tension measuring device. In FIG. 12, reference character 12 designates a spool shaft journaled rotatably on side plates 4, 5 through bearings (one bearing 14 is only shown in FIG. 12). A spool 2 with a fishline 1 wound therearound is mounted rotatably on the spool shaft 12. A spool drive gear train is mounted within the side plate 5 and, by rotating a handle 23 the spool 2 can be rotationally driven through the spool drive gear train.
The bearing 14, which supports one end portion of the spool shaft 12 on the side plate 4, is fitted into a ring-shaped support ring 61 coaxially and integrally. The support ring 61 is fitted through a highly elastic spacer member 62 such as a Teflon sheet or the like into a bearing mounting portion 24 which is formed in the central portion of the inside of the side plate 4. When fish is caught in the terminal tackles and tension is applied to the fishline 1, the support ring 61 including the bearing 14 can be moved slightly in the diametrical direction (in the tension direction of the fishline 1) according to the loads that are given to the spool shaft 12.
Now, FIG. 13 is a section view of the bearing portion of the above disclosed device. The support ring 61 includes on the outer peripheral wall thereof a projection 63 which is disposed on the opposite position to the tension applying direction of the fishline 1 (a direction of an arrow F in FIG. 13) and, to the projection 63, there is screwed one end of a rectangular strain plate 64 having a thickness of 0.3 mm and formed of a SUS material or the like. Also, a block 65 is fixed to the other end of the strain plate 64 and a screw 66 for tension, which is so supported as to extend through the side plate 4 in the diametrical direction from outside, is threadedly engaged with the block 65. Thus, by screwing the screw 66 into the block 65, a given tensile force can be applied to the strain plate 64.
On the other hand, a pair of strain gages 67, 68 and a pair of strain gages 69, 70 are bonded to the front and back surfaces of the strain plate 64, respectively. These strain gages 67, 68, 69, 70 are used to detect tensile forces in the following manner. That is, when a load is given to the spool shaft 12 due to the tension of the fishline 1 and strain is generated in the strain plate 64 according to the load, the resistance values of the strain gages 67, 68, 69, 70 are varied according to the amounts of the strain, to thereby detect the tension applied to the fishline 1.
Now, FIG. 14 is a circuit diagram of a bridge circuit made by use of the above-mentioned strain gages. The bridge circuit is used to measure the above-mentioned variations in the resistance values of the strain gages. The strain gages 67, 69 are connected in series to each other, the strain gages 70, 68 are also connected in series to each other, and DC voltages are applied to two terminals P.sub.1, P.sub.2. A connecting point P.sub.3 between the strain gages 67 and 69 and a connecting point P.sub.4 between the strain gages 70 and 68 are respectively connected to the differential inputs of a voltage amplifier 71. The output of the voltage amplifier 71 is connected to a tension display part 72.
Since the above disclosed conventional fishline tension measuring device is structured in this manner, if fish is caught in the terminal tackles of a fishing reel and tension is applied to the fishline 1, in FIG. 13, the tension acts through the spool shaft 12 on the bearing 14 and, at the same time, the tension pulls the support ring 61 including the bearing 14 in a direction of an arrow F. Due to this, the support ring 61 compresses the spacer member 62 and moves slightly in the same direction according to the tension, thereby causing the strain plate 64 to extend elastically so as to produce strain in the strain plate 64.
Thus, if the strain is produced in the strain plate 64, then the resistance values of the strain gages 67, 68, 69, 70 respectively bonded to the strain plate 64 are varied to cause the bridge circuit shown in FIG. 14 to lose its balanced state, so that there is generated a potential difference between the connecting points P.sub.3 and P.sub.4. The potential difference is in proportion to the tension applied to the fishline 1.
After the potential difference is amplified by the voltage amplifier 71, it is output to the tension display part 72 where the tension is displayed.
Therefore, if an angler sees the display of the tension display part 72, then the angler can judge the magnitude of the currently applied tension easily.
In the above-mentioned tension measuring device disclosed in the Japanese Utility Model Kokai Publication No. Sho. 64-5493, to measure tension, it is necessary to add new parts such as the support ring 61, spacer member 62, strain plate 64, block 65 and the like. This results in the complicated structure, which is difficult to assemble and increases the manufacturing cost of the measuring device.
Further, since the strain plate 64 is thin and weak in strength, the measuring device it is difficult to provide the measuring device having sufficient strength satisfactory for a fishing reel which is used in the craggy place and thus an receive strong drop shocks and the like.
Since the strain gage receives various kinds of pressure and is caused to extend repeatedly, it has problems in durability and aged deterioration. In particular, due to the strain limit and aged deterioration of an adhesive agent used for bonding the strain gage, the zero balance and reproducibility of the strain gage are changed.
Further, since the four strain gages must be bake-adhered to the strain plate, there is required a high degree of technical skill and a complicated series of processes, such as application of the adhesive agent, bonding, pressurization, terminal processing, baking, moistureproof treatment, and the like.
Furthermore, the wires for the four strain gages must be connected together in a three-dimensional manner, and the respective connecting portions thereof must be treated with an anticorrosive, which requires the higher number of manufacturing steps and results in difficulty in assembling.